DC electric motors are used in a variety of different applications and environments. In many cases, precise control of an electric motor's operational characteristics is desirable, particularly when used for bidirectional control, such as gimbal platforms.
In some applications, brushless direct current (BLDC) motors are used. Conventional commutation logic provides sequential signaling to excite the motor's windings in a manner that results in the motor's motion. In some conventional approaches, to regulate the motor's torque, pulse width modulation (PWM) control signals that occur simultaneously with the commutation logic vary the duty cycle of a high frequency waveform that is applied to cause high frequency switching (e.g., turning on or off) of switches and/or to alternately connect and disconnect a power source to/from the motor's windings. In some cases, the high frequency nature of the switching and/or connection/disconnection is effectively converted to a DC current by the smoothing provided via the motor's inductance. To adjust the current passing through the windings (e.g., and thus adjust the speed of the electric motor), duty cycles of the PWM control signals may be adjusted.
Although BLDC motors may advantageously provide high performance and reduced wear (e.g., due to the use of PWM control signals for commutation rather than brushes), the switching noise associated with the PWM control signals can interfere with sensitive electronics. For example, in servo motor applications (e.g., gyro-stabilized gimbals) and/or other applications, electric motors are often mounted in proximity to other inductive components (e.g., pancake resolvers), and wiring to motor phases are often routed through slip ring connections. Low inductance generally desired of BLDC motors in such applications may require high PWM switching frequencies (e.g., due to the low L/R time constants) to avoid excessive heating (from ripple currents) in the motor windings.
The high PWM switching noise may cause a higher rate of current change through the motor windings, which may result in cross talk between components in proximity to (e.g., adjacent to) the BLDC motors via parasitic signals coupled from the BLDC motor's windings and any wires attaching to them to these components. To avoid such crosstalk, increased inductive and/or capacitive shielding may be required in such cases. In addition, the higher rate of current change may cause higher levels of electromagnetic interference (EMI) that impacts ability of a system that uses the BLDC motors to meet conducted and radiated emission standards.
For example, a gimbal used to move sensitive equipment, such as video equipment, may couple signals from the motor windings to video signals of the video equipment, thus decreasing quality of the video signals. To avoid crosstalk due to the switching noise, additional shielding may be deployed to avoid stray inductive coupling, thus occupying space and increasing component cost. In many cases, at higher switching frequencies, the higher PWM switching noise of the BLDC motors cannot be adequately minimized to a level necessary to maintain typical performance (e.g., gimbal or pan/tilt performance) achieved with brushed motors.
Therefore, there is a need to provide improved ways to facilitate control of electric motors.